Cleaning gas device cleaning the process gas of a reflow soldering system

ABSTRACT

Disclosed is a cleaning device ( 11 ) for the processing gas of a reflow soldering system and a method for the operation thereof. According to the invention, the cleaning device contains a cleaning fluid ( 16 ) enables non-cleaned process gas ( 12 ) to be guided, e.g. in the form of rising bubbles ( 24 ). The cleaned process gas is removed from the cleaning device ( 11 ). By using a cleaning fluid to separate impurities from the process, the invention is advantageous in comparison with conventional filters in that the process gas is subjected to little flow resistance, enabling the process gas to be cleaned in an efficient, low-cost matter.

The present invention relates to a cleaning device for process gasesparticularly of a reflow soldering system, the device comprising aplurality of cleaning chambers containing a cleaning liquid for theprocess gas, each of the cleaning chambers being adapted to be flownthrough via a supply line for the contaminated process gas and adischarge line for the cleaned process gas.

Cleaning devices for reflow soldering gases are e.g. known from the USpatent provided with U.S. Pat. No. 4,951,401. Said cleaning devicescomprise a channel with the help of which the process gas is taken fromthe reflow soldering system and supplied again to the system afterhaving been cleaned by means of a filter. Impurities deriving from theprocess gas are retained by the filter, which can be replaced or washedas soon as its absorbing capacity has been exhausted. A further cleaningdevice for process gases of a reflow soldering system is described in JP59-029020 A. In this system, the process gas is passed through acleaning liquid.

A cleaning device for exhaust gases issuing from combustion processes isdescribed in DE 37 27 2943 A1. Said device comprises a tubular housingwhich can be divided by so-called gas distributor plates into severaldeposition chambers for the process gas. The number of the employed gasdistribution plates depends on the length of the tubular housing.

It is the object of the present invention to provide a cleaning devicefor the process gas particularly of a reflow soldering system with thehelp of which a comparatively efficient cleaning of the process gas canbe effected independently of the general conditions set by the system.

According to the invention this object is achieved in that the cleaningchambers are each formed by modules of which such a great number isarranged to be flown through in parallel that the required throughput ofprocess gas is achieved, and of which such a great number is arranged tobe flown through one after the other that the required degree of purityis achieved for the process gas. The impurities issuing from the processgas can be discharged to the cleaning liquid by contacting the processgas with the cleaning liquid. In this process, the cleaning device canadvantageously be adapted to the required deposition performance in anoptimum way in that the modules are connected in parallel in response tothe required throughput of process gas and in series in response to therequired residual content of impurities. It is particularly possible toconnect modules of different operative principles in series to be ableto achieve the required degree of deposition and to filter, forinstance, impurities with different properties in an optimum way. Theindividual modules employed can be configured to have a simpleconstruction and a small constructional size, so that e.g. with the helpof plug-type connections it is easily possible to create cleaningdevices offering the possibility of a finely graded capacity adaptation.

A further advantage is that the enhancement of the depositionperformance is not limited by a rise in the loss of pressure produced bythe cleaning device.

An additional advantage in the use of cleaning liquid is due to the factthat said liquid can be exchanged without the process sequence of thereflow soldering system being stopped. The removed and contaminatedcleaning liquid can here be replaced by a clean cleaning liquid at thesame time. Since standstill times of the reflow soldering system areavoided, profitability during operation of a reflow soldering systemprovided with the cleaning device according to the invention canadvantageously be enhanced.

It is advantageous when modules with different operative principles arearranged one after the other in series during deposition. In this case,it is e.g. possible to employ, first of all, an operative principle witha high absorption capacity with respect to impurities, whereby theprocess gas can first be freed within a short period of time from themajority of impurities. Subsequently, an operative principle may e.g. beemployed with a high performance with respect to the attainable residualconcentration, so that a high degree of purity of the cleaned processgas can be set.

According to a variant of the invention a flow path for the cleaningliquid extends through the series-connected modules such that thedirection of flow of the cleaning liquid is opposite to the direction offlow of the process gas. This advantageously improves the depositionperformance of the cleaning device of the invention through realizationof a counter-current principle.

According to a further variant of the module-like construction, cleaningliquids with different cleaning properties may be provided in thecleaning chambers of the parallel-connected modules. It is therebypossible to select different cleaning liquids, each being advantageouslyadapted in an optimum way to different substances to be separated.Optimum cleaning results can respectively be achieved with said cleaningliquids. When different cleaning liquids are used, it is particularlyadvantageous to series-connect the modules with respect to the processgas to be cleaned because the process gas will then pass in one cyclethrough all of the different cleaning liquids.

According to a further variant of the invention, the cleaning chambercontains a bath consisting of the cleaning liquid, the supply lineterminating below the liquid level of the bath in said bath. It isthereby possible in an advantageous way to pass the process gas in theform of bubbles through the bath, whereby the surface is enlarged thatis available for discharging the impurities from the process gas to thecleaning liquid. At the same time the construction of said cleaningmeans is very simple, whereby an inexpensive production is made possiblein an advantageous way.

According to another variant of the invention the cleaning chambercomprises at least one deposition wall on the surface of which a film ofthe cleaning liquid is provided. An exactly defined deposition surfacecan thereby be formed in an advantageous way, the deposition surfacebeing defined by the surface of the cleaning-liquid film formed on thedeposition wall.

It is advantageous when the deposition wall is arranged perpendicular orwith a slope in the cleaning chamber and when in the area of a topdeposition-wall edge which is obtained due to said arrangement, a supplymeans for the cleaning liquid is arranged that is directed thereto. Thishas the effect that the cleaning liquid flows, starting from the topedge of the deposition wall in the manner of a waterfall and inconformity with gravity, downwards along said wall, and the cleaningliquid can thus be replaced without any problems.

According to another variant of the invention, at least one injectionopening for the cleaning liquid is directed into the cleaning chamber.The cleaning liquid can be distributed by means of preferably aplurality of injection openings in the cleaning chamber, whereby amixture is formed with the process gas to be cleaned. Advantageously,the surface which is available for absorbing impurities in the cleaningfluid is thereby enlarged. For instance, a liquid curtain can be formedthrough which the process gas is passed. The injection openings,however, may also be configured in the form of nozzles, so that a liquidmist can be produced in the cleaning chamber.

A further variant of the invention is characterized by a combination ofseveral modules, each containing a cleaning chamber, in such a mannerthat a process gas can flow through all of the cleaning chambers. It ishere possible to achieve the combination, on the one hand, as a parallelconnection of a plurality of modules, whereby the capacity of thecleaning device can advantageously be adapted to different reflowsoldering systems. The constructional efforts are here small and thereduction of individual components has an advantageous effect on storagein the marketing of the cleaning device. Another possibility is providedby the series-connection of modules, whereby the cleaning device can bemodified with respect to the quality of the deposition result.Particularly modules with different operative principles, e.g. themodules already described above, can be connected one after the other,so that the advantages of the individual operative principles can becombined with one another.

Advantageously, the cleaning chamber may comprise an outlet which isconnected to a clarifying device for the cleaning liquid. The clarifyingdevice may e.g. consist of a clarifying tank in which the impuritiesintroduced into the cleaning liquid can settle as sludge. This sludgecan then be disposed off easily while the clarified cleaning liquid canbe returned again to the cleaning process. This offers the possibilityof using the cleaning liquid repeatedly, whereby profitability duringoperation of the cleaning device can be further enhanced in anadvantageous manner.

Further details of the invention shall now be described in the followingwith reference to the drawing, in which

FIG. 1 shows one possibility of connecting a cleaning device to a reflowsoldering system, in a schematic section;

FIGS. 2 to 4 shows possible operative principles for cleaning deviceswith a cleaning liquid, in a schematic section; and

FIG. 5 is a schematic and partly cut-open illustration of an embodimentof the cleaning device according to the invention in a modulararrangement.

FIG. 1 shows a cleaning device 11 which is connected via a supply line12 and a discharge line 13 to a reflow soldering system 14 in such amanner that the process gas contained in the reflow soldering system issupplied to the cleaning device in the manner as outlined by arrows andcan be returned into the reflow soldering system 14 after the cleaningprocess has been carried out, resulting in a circulatory flow for theprocess gas. The cleaning device includes a cleaning chamber 15 which ispartly filled with a cleaning liquid 16. At an interface 17 between thecleaning liquid 16 and the process gas contained in the cleaning chamber15, impurities are exchanged from the process gas into the cleaningliquid.

With a clarifying device 18 in the form of a clarifying tank, thecleaning liquid 16 forms a circulatory flow which is completed via asupply 19 to the cleaning device and via an outlet 20 away from thecleaning device. In the clarifying device 18, the impurities transferredfrom the process gas into the cleaning liquid 16 settle down as sludge21. The sludge can be removed via an outlet valve 22 from the clarifyingdevice.

Inert liquids such as water or oils may e.g. be used as cleaningliquids, said liquids being non-reactive with constituents of theprocess gas. Of particular advantage is the use of so-calledperfluoropolyethers, which are soluble neither in water nor in oil andare characterized by a high resistance to reactive chemicals.

Further embodiments of cleaning means shall be explained in thefollowing; components which are configured in accordance with theembodiment shown in FIG. 1 are provided with the same reference numeralsand shall not be explained in more detail.

The cleaning device 11 according to FIG. 2 is of a cylindricalconfiguration and is predominantly filled with the cleaning liquid 16.The cleaning liquid is continuously exchanged via inlet 19 and outlet20.

The process gas is supplied via the supply line 12 and a distributor 23below the liquid level of the cleaning liquid 16, so that the processgas can be cleaned while rising upwards in small bubbles 23 in thecleaning liquid.

Deposition walls 25, which are partly formed by the outer wall of thecleaning device 11 at the same time, are provided in the cleaningchamber 15 of the cleaning device 11 according to FIG. 3. Supply means27 which are connected to the supply for the cleaning liquid (not shownin more detail in FIG. 3) are provided on the upper edges 26 of thedeposition walls. As outlined, the supply means 27 wet the depositionwalls 25 with the cleaning liquid, so that said liquid flows down alongthe walls and is collected in the lower portion of the cleaning deviceat outlet 20. A film 28 of the cleaning liquid is formed in this processon the deposition walls 25, with the process gas sweeping along saidfilm.

The cleaning device 11 shown in FIG. 4 is provided in the cleaningchamber 15 with a plurality of injection openings 29 which are connectedto supply 19. The injection openings in their entirety produce a rain-or mist-like curtain 30 in the cleaning chamber 15, the process gasbeing passed through said curtain. The cleaning liquid is collected inthe lower part of the cleaning chamber in the area of outlet 20.

FIG. 5 shows a modular construction of the cleaning device 11 by way ofexample. Modules 31 a, 31 b are represented in a simplified manner asboxes, two of said boxes being cut open. As can be seen from theillustrated cut-open modules, two modules with different operativeprinciples are series-connected each time. Modules 31 a have apre-cleaning function and employ the operative principle shown in FIG.2. Modules 31 b have a final cleaning function, the operative principleof FIG. 4 being here employed. Of course, any other desired combinationof operative principles is possible.

The cleaning liquid is first supplied to modules 31 b and then tomodules 31 a. Therefore, a cleaning liquid slightly subjected toimpurities is first available for the final cleaning process, wherebythe efficiency of the final cleaning process is improved. The cleaningliquid is subsequently used for the pre-cleaning process where acleaning effect is possible due to the still high concentration ofimpurities in the process gas. As for the flow directions of cleaningliquid and process gas, the counter-current principle is thus realizedaccording to FIG. 5. However, a co-current principle is just as wellpossible if this seems to be more appropriate for the specific case ofapplication. Moreover, it is also possible to use different cleaningliquids in modules 31 b and 31 a for subjecting the process gas insuccessive order to different cleaning steps (not shown).

While the series-connection of the modules 31 a and 31 b improves thecleaning action of the cleaning device 11, the parallel arrangement ofthe respective module combination 31 a, 31 b aims at an enhancement ofthe possible throughput of process gas. As a consequence, the modularcleaning device 11 can be adapted to reflow soldering systems havingdifferent capacities.

1. A cleaning device for process gases that generates clean process gasfrom contaminated process gas in a reflow soldering system comprising: aplurality of cleaning chambers containing a cleaning liquid for saidprocess gas, each of said cleaning chambers allowing the contaminatedprocess gas to flow therein via a supply line and allowing the cleanedprocess gas to flow therefrom via a discharge line, wherein the cleaningchambers are each formed by a plurality of modules in parallel to allowfor a predetermined throughput and in successive order to allow for apredetermined degree of purity for the process gas.
 2. The cleaningdevice according to claim 1, wherein the plurality of modules includemodules having different operative principles of deposition that areconnected one after the other in series.
 3. The device according toclaim 2, wherein a flow path for the cleaning liquid extends through theseries-connected modules in such a manner that the direction of flow ofthe cleaning liquid is opposite to the direction of flow of the processgas.
 4. The cleaning device according to claim 1, wherein the cleaningliquids have different cleaning properties, such that respective ones ofwhich are provided in respective ones of the plurality of cleaningchambers of the Modules arranged in the successive order.
 5. Thecleaning device according to claim 1, wherein at least a part of each ofthe plurality of cleaning chambers contains a corresponding bathincluding the cleaning liquid, the supply line coupled below the liquidlevel of the bath.
 6. The cleaning device according to claim 1, whereinat least a part of each of the plurality of cleaning chambers containsat least one deposition wall on a surface of which a film of thecleaning liquid is positioned.
 7. The cleaning device according to claim6, wherein the deposition walls are arranged perpendicular or with aslope with respect to each other in the plurality of cleaning chambersand the supply means for the cleaning liquid are arranged in an area ontop of edges of the deposition walls.
 8. The cleaning device accordingto claim 1, wherein at least one respective injection opening for thecleaning liquid is directed into at least part of each of the pluralityof cleaning chambers.
 9. The cleaning device according to claim 1,wherein at least part of each of said plurality of cleaning chamberscomprise a respective outlet that is connected to a clarifying devicefor the cleaning liquid.